1. Field of the Invention
The present invention relates to a spread illuminating apparatus of side light type, and particularly to a spread illuminating apparatus which has a structure in which a light conductor plate and a housing frame are integrated with each other.
2. Description of the Related Art
A liquid crystal display (LCD) device which is characterized by having a small thickness, a small occupation volume, a light weight and the like is used extensively in various electric products, such as a mobile telephone and a personal computer. Since a liquid crystal in the LCD device does not emit light by itself, a lighting means to light its display area is provided in many LCD devices. Recently, while the thickness of the LCD device is requested to be further reduced, the display area of the LCD is requested to be increased, and in order to satisfy these requests, the lighting means must be reduced in thickness and also in power consumption.
In order to achieve reduction of thickness and consumption of the lighting means, a point light source, for example, an LED is used as a light source of the lighting means, and constituent members of the lighting means, such as a light source, a light conductor plate and the like, are fixedly disposed in place thereby efficiently utilizing light.
For example, as shown in FIG. 16, LEDs 2 and a rectangular light conductor plate 1 to receive lights from the LEDs 2 and to emit illumination light are disposed in place within a housing frame 7 made of a white resin. Protrusions 12a and 12c are provided at each of side surfaces 11 and 12 of the light conductor plate 1 orthogonal to a side surface 8 having the LEDs 2. The light conductor plate 1, when placed within the housing frame 7, is positioned and also fixed by the protrusions 11 and 12. Recesses 20a and 20c are formed at the housing frame 7, and the protrusions 12a and 12c of the light conductor plate 1 are engagingly fitted in the recesses 20a and 20c, whereby the light conductor plate 1 is held by the housing frame 7 (refer, for example, to Japanese Patent Application Laid-Open No. 2005-302485).
However, in the structure where the rectangular light conductor plate 1 is disposed in place within the housing frame 7, a gap is required between the perimeter of the light conductor plate 1 and the inner perimeter of the housing frame 7 in view of the engaging connection therebetween, and light loss caused by the gap must be made up for by some measures. Also, the white resin to form the housing frame 7 has a smaller reflectance than a reflector constituted by a reflection film such as en ESR (Enhanced Specular Reflector) (refer, for example, to PCT Application published under No. H9-506837) which produces another cause for light loss thus requiring another measures to make up for light loss.
Moreover, when the spread illuminating apparatus described above is further reduced in thickness, the entire rigidity becomes insufficient, and also it is likely to happen that the protrusions 12a and 12c of the light conductor plate 1 disengage from the recesses 20a and 20c of the housing frame 7.
Under the above circumstances, another conventional spread illuminating apparatus is disclosed, which is adapted to achieve a sufficient mechanical strength while achieving reduction of thickness, and which has an integrated structure of a light conductor plate portion 421 and a housing frame portion 422 as shown in FIG. 17. In FIG. 17, a pattern 426 is formed at a predetermined distance from light sources 410, 410 (refer, for example, to Japanese Patent Application Laid-Open No. 2006-285171).
In the example in FIG. 17, however, the housing frame portion 422 is to be made of a resin material which has a high optical transmittance like that of the light conductor plate portion 421, and therefore light is caused to leak from the housing frame portion 422. If such light leakage occurs, not only the brightness of the spread illuminating apparatus is lowered, but also the leakage light possibly results in deteriorating the appearance of a device such as a mobile telephone in which the spread illuminating apparatus is incorporated.
In order to overcome the problems described above, in an example shown in FIG. 17 grooves 425 are provided at portions of the light conductor plate portion 421 located close to the housing frame portion 422, and lights emitted from the light source 410 and 410 and traveling in the light conductor plate portion 421 are totally reflected by the grooves 425, whereby the lights are prevented from leaking outside.
However, since polycarbonate or polymethylmethacrylate that is a common resin material for a light conductor plate has a refractive index of about 1.5 and has a relatively large critical angle, it may potentially happen depending on the design of constituent members that the rate of light is increased which travels toward the grooves 425 at an angle smaller than the critical angle of the resin material, resulting in that the grooves 425 fail to adequately prevent the lights from leaking by means of total reflection.
Further, the grooves 425 are not continuous to one another, but bridging portions 427 are provided which each connect between two adjacent grooves 425 thereby ensuring a necessary mechanical strength of the apparatus. Some lights traveling in the light conductor plate portion 421 enter the housing frame portion 422 through the bridging portions 427 thus significantly causing light leakage.
Also, in the example of FIG. 17, for preventing light leakage from the housing frame portion 422, a reflective film must be fixedly attached to the outer side surfaces of the housing frame portion 422 by some kind of method, and, for example, if a double face tape is used for fixed attachment, light is absorbed by the adhesive layers of the double face tape. Even if the reflective film can be fixedly attached to the outer side surfaces of the housing frame portion 422 without using a double face tape, light is inevitably absorbed and lost to some extent while traveling in the housing frame portion 422.